The present invention relates to air dryers. It finds particular application in conjunction with air dryers used on vehicles and will be described with particular reference thereto. It will be appreciated, however, that the invention is also amenable to other applications.
Air dryers are used, for example, on heavy vehicles for drying compressed air delivered from a compressor to a vehicle operating storage reservoir for use in operating various systems on the vehicle that utilize compressed air. One type of air dryer includes a cartridge, which includes a desiccant material through which the compressed air passes while being dried. The cartridge is secured to an air dryer housing, most commonly via a threaded connection.
As the compressor provides air during a charging cycle, the desiccant becomes saturated with moisture and other contaminants that are removed from the compressed air. At the end of the charging period the air dryer is switched into a regeneration mode during which previously dried compressed air is circulated back through the desiccant material. As the dried air passes through the desiccant, the moisture and contaminants in the desiccant are captured in the airflow and thereby removed from the desiccant. The air including the moisture and contaminants is then expelled (e.g., exhausted) from the air dryer. After the regeneration mode is complete, the air dryer can once again execute a charge cycle.
In older air dryer systems, air from the vehicle operating storage reservoir is used during the regeneration cycle. Such air, however, may not be sufficiently dry and clean to effectively regenerate the desiccant since it the performance of the desiccant decreases during the charge cycle and the air then recirculated through the desiccant is from the tail end of the charge cycle when the desiccant is less effective.
Thus, it has been found desirable to store the driest and cleanest air from that charge cycle in a regeneration storage volume separate from the vehicle operating storage volume. In this regard, air dryer systems have been developed wherein the first air passing through the desiccant at the beginning of a charge cycle is stored in the regeneration storage volume. In some systems, a valve is included internal to the air dryer that is operative to channel the initial flow from the dryer cartridge to the regeneration storage volume. Once the regeneration storage volume is filled, the valve then operates to channel air to the vehicle operating storage volume.
In commonly-assigned U.S. Pat. No. 7,520,922, such valving is included in a removable dryer cartridge, separate from the air dryer unit. The cartridge disclosed in the '922 patent includes a desiccant volume, a desiccant in the desiccant volume for removing at least one of moisture and contaminants from air, a first passage in fluid communication with the desiccant volume and a first air storage volume (e.g., a regeneration storage volume), a second passage in fluid communication with the desiccant volume and in fluid communication with a second air storage volume (e.g., a vehicle operation storage volume), and a valve which, in a first position, restricts the fluid communication between the desiccant volume and the first air storage volume.
Although the desiccant in either type of system is frequently regenerated in the manner described above, it is to be understood that the desiccant degrades over time due to the presence of contaminants (e.g., oil) in the incoming air stream. In fact, more and more residual oil and contaminants can be retained in the desiccant after each regeneration cycle. Therefore, over time, the desiccant becomes oil saturated such that it cannot be satisfactorily regenerated by the regeneration cycle described above. Although the life of the desiccant may be extended by improved purge functionality, at some point, the desiccant must be replaced. To this end, a spent cartridge may be replaced with anew cartridge containing fresh desiccant.
The process for replacing the dryer cartridge is generally straightforward and typically involves unscrewing the spent cartridge and threading-on the proper replacement cartridge depending on whether the air dryer system being serviced has the internal valving or the cartridge valving as the system described in the '922 patent. As will be appreciated, to avoid consumers installing the wrong cartridge on an air dryer unit, a standard thread size has evolved wherein a 39 mm thread size is used in the industry for standard cartridges designed for air dryer units having the internal valving. A cartridge having the internal valving, such as that disclosed in the '922 patent, has a different size thread diameter (e.g., 31 mm). Thus, cartridges containing the valving will not fit a dryer having the internal valve arrangement, and vice versa. This ensures that only the proper replacement cartridge is installed on a given air dryer unit, but requires the manufacture of separate cartridges to fit both types of air dryer systems.